1. Field of the Invention
The invention is directed to a method of manufacture of metallic products such as aluminide metal sheets and an apparatus for performing the method. More particularly, the invention is directed to a hot forming operation that forms the metallic product geometry and tempers the product in a unitary step.
2. Background of the Invention
In the description of the background of the present invention that follows, reference is made to certain structures and methods, however, such references should not necessarily be construed as an admission that these structures and methods qualify as prior art under the applicable statutory provisions. Applicants reserve the right to demonstrate that any of the referenced subject matter does not constitute prior art with regard to the present invention.
In a resistive heating assembly, such as a resistive heating assembly as disclosed in commonly assigned U.S. Pat. Nos. 5,530,225, 5,591,368, 5,665,262, and 5,750,964 for an electrical heater cigarette smoking system (EHCSS), a heater having a plurality of heater blade arrays can be resistively heated by passing a current therethrough. FIG. 1 shows a representative metallic part 100 of a resistive heating assembly. Heater blades 102 extending from and attached to a supporting hub 104 can be either single legs or multiple legs (i.e., two legs). The heater blades 102 are arranged to form an open cylindrical shaped heater fixture to accommodate a cigarette inserted therein. The heater blades 102 are preferably curved at intermediate portions 106 thereof such that a cigarette is contacted by the intermediate portions, i.e., the heater blade assembly is hour-glass shaped such that insertion of a cigarette into an open end 108 causes the heater blades 102 to expand outwardly when the cigarette is pushed through the intermediate portions 106 towards the hub 104.
Heater blades and heater blade arrays of an iron aluminide alloy have previously been made by cold forming a sheet and cutting the sheet into a heater array blank. The heater array blank comprised heater blades attached at the hub and had a carrier strip maintained on an opposite end of the sheet to facilitate handling. Subsequently, the heater array blank was formed into a substantially cylindrical shape, welded in a bonding apparatus, and formed to a final desired shape. The formed and bonded heater array was then tempered in an independent discrete step from the forming operation by contact with a heat sink (i.e., insertion of a straight ceramic rod) into the center portion of the cylindrical heater array and increasing the temperature of the heater array blades by the passing of an electrical current therethrough. The electrical current heated the array above a certain temperature and the heat sink quenched the array.
Several difficulties have been encountered with this production method. For example, the cold forming and cutting of the heater array blank resulted in a deformed final shape (e.g., misaligned heater blades and protruding heater blade legs). During the bonding or welding step, the individual heater blades misaligned causing the final tolerance of the heater array blank to be greater than acceptable. Misalignment resulted in a non-centered circular heater array assembly, and, after removal of the carrier strip, the final heater array shape was not maintained. Therefore, overall yield on the product was reduced, in some instances as much as 50% reduced. Moreover, the quenching operation of the heater array blank was performed in a separate processing step, complicating and adding expense to the manufacturing process.
Therefore, there is a need for a method of processing a metallic part in which the final tolerances are within an acceptable value, and resulting in a higher yield of the products produced. Further, it is desirable to minimize the number of operations in the assembly process by combining the thermomechanical operations into a minimum number of steps.